Neuronal stimuli are transmitted by the central nervous system (CNS) through the interaction of a neurotransmitter released by a neuron, which neurotransmitter has a specific effect on a neuroreceptor of another neuron. L-glutamic acid is considered to be a major excitatory neurotransmitter in the mammalian CNS, consequently playing a critical role in a large number of physiological processes. Glutamate-dependent stimulus receptors are divided into two main groups. The first group comprises ligand-controlled ion channels whereas the other comprises metabotropic glutamate receptors (mGluR). Metabotropic glutamate receptors are a subfamily of the G-protein-coupled receptors (GPCR). There is increasing evidence for a peripheral role of both ionotropic and metabotropic glutamate receptors outside the CNS e.g. in chronic pain states.
At present, eight different members of these mGluRs are known. On the basis of structural parameters such as sequence homology, the second messenger system utilized by these receptors and their different affinity to low-molecular weight compounds, these eight receptors can be divided into three groups. MGluR1 and mGluR5 belong to Group I which are positively coupled to phospholipase C and their activation leads to a mobilization of intracellular calcium ions. MGluR2 and mGluR3 belong to Group II and mGluR4, mGluR6, mGluR7 and mGluR8 belong to Group III, both of which are negatively coupled to adenylyl cyclase, i.e., their activation causes a reduction in second messenger cAMP and thus a dampening of neuronal activity.
The mGluR5 modulators have been shown to modulate the effects of the presynaptically released neurotransmitter glutamate via postsynaptic mechanisms. Moreover, as these modulators can be both positive and/or negative mGluR5 modulators, such modulators may increase or inhibit the effects mediated through these metabotropic glutamate receptors.
Of particular interest are those modulators which are negative mGluR5 modulators. Such modulators decrease the effects mediated through metabotropic glutamate receptors. Since a variety of patho-physiological processes and disease states affecting the CNS are thought to be related to abnormal glutamate neurotransmission, and mGluR5 receptors are shown to be expressed in several areas of the CNS, modulators of these receptors could be therapeutically beneficial in the treatment of CNS diseases.
Therefore, mGluR5 positive or negative modulators may be administered to provide neuroprotection and/or disease modification in the following acute or chronic pathological conditions or to provide a symptomatological effect on the following conditions:
Alzheimer's disease, Creutzfeld-Jakob's syndrome/disease, bovine spongiform encephalopathy (BSE), prion related infections, diseases involving mitochondrial dysfunction, diseases involving β-amyloid and/or tauopathy, Down's syndrome, hepatic encephalopathy, Huntington's disease, motor neuron diseases, amyotrophic lateral sclerosis (ALS), olivoponto-cerebellar atrophy, post-operative cognitive deficit (POCD), systemic lupus erythematosus, systemic sclerosis, Sjogren's syndrome, Neuronal Ceroid Lipofuscinosis, neurodegenerative cerebellar ataxias, Parkinson's disease, Parkinson's dementia, mild cognitive impairment, cognitive deficits in various forms of mild cognitive impairment, cognitive deficits in various forms of dementia, dementia pugilistica, vascular and frontal lobe dementia, cognitive impairment, learning impairment, eye injuries, eye diseases, eye disorders, glaucoma, retinopathy, macular degeneration, head or brain or spinal cord injuries, head or brain or spinal cord trauma, trauma, hypoglycaemia, hypoxia, perinatal hypoxia, ischaemia, ischaemia resulting from cardiac arrest or stroke or bypass operations or transplants, convulsions, epileptic convulsions, epilepsy, temporal lobe epilepsy, myoclonic epilepsy, inner ear insult, inner ear insult in tinnitus, tinnitus, sound- or drug-induced inner ear insult, sound- or drug-induced tinnitus, L-dopa-induced dykinesias, L-dopa-induced dykinesias in Parkinson's disease therapy, dyskinesias, dyskinesia in Huntington's disease, drug induced dyskinesias, neuroleptic-induced dyskinesias, haloperidol-induced dyskinesias, dopaminomimetic-induced dyskinesias, chorea, Huntington's chorea, athetosis, dystonia, stereotypy, ballism, tardive dyskinesias, tic disorder, torticollis spasmodicus, blepharospasm, focal and generalized dystonia, nystagmus, hereditary cerebellar ataxias, corticobasal degeneration, tremor, essential tremor, abuse, addiction, nicotine addiction, nicotine abuse, alcohol addiction, alcohol abuse, opiate addiction, opiate abuse, cocaine addiction, cocaine abuse, amphetamine addiction, amphetamine abuse, anxiety disorders, panic disorders, anxiety and panic disorders, social anxiety disorder (SAD), attention deficit hyperactivity disorder (ADHD), attention deficit syndrome (ADS), restless leg syndrome (RLS), hyperactivity in children, autism, dementia, dementia in Alzheimer's disease, dementia in Korsakoff syndrome, Korsakoff syndrome, vascular dementia, dementia related to HIV infections, HIV-1 encephalopathy, AIDS encephalopathy, AIDS dementia complex, AIDS-related dementia, major depressive disorder, major depression, depression, depression resulting from Borna virus infection, major depression resulting from Borna virus infection, bipolar manic-depressive disorder, drug tolerance, drug tolerance to opioids, movement disorders, fragile-X syndrome, irritable bowel syndrome (IBS), migraine, multiple sclerosis (MS), muscle spasms, pain, chronic pain, acute pain, inflammatory pain, neuropathic pain, diabetic neuropathic pain (DNP), pain related to rheumatic arthritis, allodynia, hyperalgesia, nociceptive pain, cancer pain, posttraumatic stress disorder (PTSD), schizophrenia, positive or cognitive or negative symptoms of schizophrenia, spasticity, Tourette's syndrome, urinary incontinence, vomiting, pruritic conditions, pruritis, sleep disorders, micturition disorders, neuromuscular disorder in the lower urinary tract, gastroesophageal reflux disease (GERD), gastrointestinal dysfunction, lower esophageal sphincter (LES) disease, functional gastrointestinal disorders, dyspepsia, regurgitation, respiratory tract infection, bulimia nervosa, chronic laryngitis, asthma, reflux-related asthma, lung disease, eating disorders, obesity, obesity-related disorders, obesity abuse, food addiction, binge eating disorders, agoraphobia, generalized anxiety disorder, obsessive-compulsive disorder, panic disorder, posttraumatic stress disorder, social phobia, phobic disorders, substance-induced anxiety disorder, delusional disorder, schizoaffective disorder, schizophreniform disorder, substance-induced psychotic disorder, or delirium.
The mGluR5 negative or positive modulators may also be administered to provide inhibition of tumour cell growth, migration, invasion, adhesion and toxicity in the peripheral tissues, peripheral nervous system and CNS. MGluR5 modulators may be administered to provide therapeutic intervention in neoplasia, hyperplasia, dysplasia, cancer, carcinoma, sarcoma, oral cancer, squamous cell carcinoma (SCC), oral squamous cell carcinoma (SCC), lung cancer, lung adenocarcinoma, breast cancer, prostate cancer, gastric cancer, liver cancer, colon cancer, colorectal carcinoma, rhabdomyosarcoma, brain tumour, tumour of a nerve tissue, glioma, malignant glioma, astroglioma, neuroglioma, neuroblastoma, glioblastoma, medulloblastoma, cancer of skin cells, melanoma, malignant melanoma, epithelial neoplasm, lymphoma, myeloma, Hodgkin's disease, Burkitt's lymphoma, leukemia, thymoma, and other tumours.
Further indications for mGluR5 negative or positive modulators include those indications wherein a particular condition does not necessarily exist but wherein a particular physiological parameter may be improved through administration of the instant compounds, for example cognitive enhancement, learning impairment and/or neuroprotection.
Positive modulators may be particularly useful in the treatment of positive and negative symptoms in schizophrenia and cognitive deficits in various forms of dementia and mild cognitive impairment.
In the literature, several types of modulators of mGluR5 have already been described.
Furthermore, several types of pyrazolopyrimidine compounds have been disclosed in the prior art.
Various methods for preparing substituted pyrazolopyrimidine derivatives are known, e.g. from G. Hajos and Z. Riedl, Science of Synthesis 109, 613-678 (2002) and from Laura Bettinetti (Ph. D. Thesis, University of Erlangen, Germany, 2004).
In WO 2004/087153 various pyrazolopyrimidines of formula (XXII) are described, which can act as small molecule immune potentiators (SMIP) and which can be used e.g. for cancer treatment.

Furthermore, in WO 2004/089471, the use of substituted pyrazolo[1,5-a]pyrimidines or prodrugs or salts thereof are described for the preparation of a pharmaceutical composition for the treatment of disorders and diseases where it is desirable to modulate the activity of the enzyme 11βHSD1 or to inhibit 11βHSD1. In the document WO 2004/089471, pyrazolo(1,5-a)pyrimidine derivates of the following general formula (C) are disclosed:

In WO 2003/037900, further specific pyrazolopyrimidine compounds are described as inhibitors of ion-channels in human cells. In this document compounds having the following general formula (X) are described:
                wherein        R1 is e.g. alkyl; R2 is a e.g. hydrogen or alkyl; or        R1 and R2 taken together with the nitrogen atom to which they are optionally joined to form a 4- to 8-membered heterocycloaryl ring;        R3 is e.g. hydrogen, alkyl, halo, amino or aryl;        R4 is e.g. hydrogen, halo, alkyl or aryl; and        R5 is a member selected from substituted or unsubstituted alkyl, substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl and substituted or unsubstituted heterocycloalkyl; R6 is e.g. hydrogen, halo or aryl; and        X is a member selected from O and S.        
Several pyrazolopyrimidine compounds according to the present invention, however have been tested which are found to be not significantly active as inhibitors of ion-channels in human cells. In this document WO 2003/037900, compounds of the following two structures are mentioned as example compounds (B308) and (B310), which however have shown no particular activity as metabotropic glutamate receptor (mGluR5) modulators:
